Several methods are known for quick charging of batteries, where the charging current is periodically interrupted and during the pause on charging a short discharge or a load is applied to the battery to be charged. The aim at these methods is to reduce the duration of charging as much as possible and to increase the lifetime of the battery by the proper maintenance and formation of the storing cells.
The charge storing capacity of a battery is specified by Ah ampere-hours. From this value a C5 value is derived by dividing it by the time=ampere-hour/hour, so C5 has a current dimension. The charging current of the battery is determined in proportion of C5. For example, for a battery having 55 Ah capacity, C5=55 A. The proper charging current of the battery is given in proportion of C5, for example 0, 1·C5, in this case 5,5 A. In the following description we use the term C5 in accordance with this definition.
In the U.S. Pat. No. 5,600,226 patent specification a method for controlling and terminating the charging of a battery is described. In the course of this method the voltage is periodically measured at the terminals of the battery and compared with the result of the preceding such measurement, then based on the difference of these two measurements the charged state level of the battery is being determined. With this known solution, the charging is periodically interrupted and during the pause of charging the measurements are performed after a short discharge pulse. At the beginning the charging is performed slower than the final charging rate, at about 20% of this final rate, then by increasing the charging pulse width the charging rate is increased to the definitive charging rate. This method has been developed before all to terminate the charging method at that point at which the battery has attained a full charge. A rapid charging of the battery is realized as well.
A similar rapid charging method is disclosed in the international patent application no. WO 00/76050 A1, in that solution however two successive discharge pulses are applied in every charging interval. After each of the two successive discharge pulses measurements are performed, to collect more accurate data on the state of the rechargeable battery.
The object of the invention is to provide a method and apparatus by means of which a faster charging of rechargeable batteries can be achieved, than with the known methods.